The present invention is related to a paint dosage device, preferably adapted for mounting in close proximity to a spray gun, and for use in a program controlled spray painting installation. The paint dosage device provides for a dosed paint supply to the spray gun, and in particular for the case in which the spray gun is provided with high tension electrode for electrical atomizing of the supplied electrically conductive paint.
As dosage means for paint supply for solvent borne, non-conductive paint fluid materials to spray guns, cogwheel pumps, dosage by a regulator combined with a measurement device, for example gear meter or other type of flow measurement or the like are used. These solutions are not applicable to application of charged conductive paint materials such as water borne paint. Application of conductive or water borne paints requires an effective insulation or galvanic blocking between a spray gun/applicator charged with a high voltage and a paint dosing device and/or the paint lines supplying the dosing device.
U.S. Pat. No. 4,785,760 (Tholome), entitled Sprayer installation, describes a sprayer installation that includes a multi-axis robot carrying a spray gun which is suitable for spraying water-based paint. The robot is equipped with a refillable tank arranged on the arm of the robot, near the end with the spray gun. The robot can move the spraying arm, and thus the tank attached to it, over to one side of a paint booth and connect the tank to one of a series of filling or cleaning lines fixed on the wall of the booth. High voltage supply to the spray gun or applicator is switched off when the robot stops spraying, and subsequently switched on again when the filling or colour change or cleaning etc. of the tank has been completed. A disadvantage with this type of solution is that it requires cleaning of the tank when carrying out a colour change and will therefore require a rather long cycle time for cleaning and refilling, in addition to the time necessary for the robot to move to a filling or cleaning station and move back to and re-orient with objects on a painting line. In addition, the demands for uninterrupted production and flexible manufacturing have led to an increased demand for rapid colour changes and/or cleaning operations, which could be a drawback with the described solution in U.S. Pat. No. 4,785,760.
U.S. Pat. No. 5,630,552, (Anfindsen) entitled Paint dosage device for program controlled spray painting system, describes a spray painting installation particularly suitable for the application of electrostatically atomized paint. The dosage device of the installation comprises dosing cylinders. Each dosage cylinder has a regulating piston, respectively, and regulation members for controlling the position and displacement velocity of the regulating pistons in the dosing cylinders. The dosing cylinders also have a controlled valve assembly and connection means for connecting the cylinders alternately to the spray gun and for connecting the cylinder when disconnected from the gun in connection with means for cleansing and refilling of paint. The spray gun may also be provided with a high tension electrode for electrostatically charging the supplied electrically conductive paint, in which case the paint is atomized by means of supplied atomizing air to the gun, the cloud formed by atomized paint particles being suitable shaped for the purpose by a beam of formation air, which also is supplied to the spray gun. The paint being conductive and in contact with the high tension electrode of the spray gun in the present case, the regulation piston of each cylinder is for that reason isolated from its associated driving motor by means of a shaft member made of electrically insulating material. The dosage device described may be mounted in close proximity to a spray gun on a robot arm, it provides accurate dosing of fluid materials (paint) and it is insulated from the paint supply lines.
A disadvantage with the above solution is that the galvanic blocking solution of applying a combination of a blocking device (insulated plunger) and an insulation fluid may be a rather complex solution which could require periodic cleaning of the insulation fluid in order to avoid a build up of any contamination by conductive particles (from paint materials).
Demands for uninterrupted coating production and flexible manufacturing of products, which typically involves shorter production runs, have led to an increased demand for faster, less time consuming colour changes and/or cleaning operations. In addition the paint dosing apparatus must also be well insulated, explosion-proof and reliable, without being excessively difficult or expensive to implement.